CXCL12 and rheumatoid arthritis: The most abundant sublining cluster, SA−0: CXCL12+ HLA-DRhi sublining fibroblasts, was a proinflammatory cluster marked by CXCL12, HLA-DRA, and CD74 accessibility and expression; SA−0 also expressed IL6, which is an established RA drug target7,8 (Fig. 3b; Supplementary Fig. 4b).